Spiral heat exchanger



3 Sheets-Sheet 1 Filed July 14, 1950 6004 4 6315 T0 jrACK VT T E r r/ 30% 0 0 I Z w M AI I P. S. OTTEN SPIRAL HEAT EXCHANGER Dec. 22, 1953 :5 Sheets-Sheet 2 Filed July 14, 1950 l I l I ll Illllllll rlllli M T N N Z W 5 p I M H P Dec. 22, 1953 P. s. OTTEN SPIRAL HEAT EXCHANGER 3 Sheets-Sheet 3 Filed July 14, 1950 INVENTOR PHIL/ 5. OTTEN Patented Dec. 22, 1953 UNITED S'E'AS TENT OFFICE SPIRAL HEAT EXCHANGER Application July 14, 1950, Serial No. 173,793

4 Claims.

This invention relates to heat exchangers of the type particularly adapted for utilizing the heat in hot fiue gases to heat air to supply the forced draft for the furnace or for other purposes.

The principal object of the invention is to provide a heat exchanger wherein a large area of heat transfer surface in a relatively small space is e iciently utilized.

A further object of the invention is-to provide a heat exchanger of the character described which can be cheaply made of sheet metal without expensive machine work or extensive hand labor. 4 further object of the invention is to provide a heat exchanger of the class described wherein the sheet metal heat transfer elements may readily expand and contract with changes in temperature.

A further object of the invention is to provide a heat exchanger of the type disclosed wherein a hi h rate of heat transfer is maintained by imparting high velocities to the two fluids in heat exchange relation.

A further object of the invention is to provide a heat exchanger of the class described which is adapted to be readily installed in the fines leading from the furnace to the stack.

Other objects of the invention will app-ear from the following specification and accompanying drawings wherein I have illustrated a typical heat exchanger embodying my improvements and also certain modifications thereof.

Referring to the drawings,

Figure 1 is a vertical sectional view of my improved heat exchanger on line 1-! of Fig. 2;

Fig. 2 is a sectional view on line 2-2 of Fig. 1;

Fig. 3 is a similar view on line 3-3 of Fig. 1;

Fig. 4 is an enlarged horizontal sectional view of a portion of the-heat exchanger showing a modified form whereby an extended heat transfer surface is obtained;

Fig. 5 is a vertical sectional view on line 5-5 of Fig. 4;

Fig. 6 is a vertical sectional view on line 6-6 of Fig. 4;

Fig. '7 is a vertical sectional view of a portion of the heat exchanger showing a further modification;

Fig. 8 is a horizontal sectional view on line 8-8 of Fig. 7.

Fig. 9 is a horizontal section of a portion of a heat exchanger showing a further modification;

Fig. 10 is a vertical sectional view on line Ill-l 0 of Fig. 9;

Fig. 11 is a horizontal sectional .view of la portion of the heat exchanger wherein the structures of Fig. 4 and Fig. 9 are combined in one installation; and V Fig. 12 is a vertical sectional view on line I2--I2 of Fig. 11.

Referring to the drawings, particularly to Figs. 1, 2 and 3, l indicates a portion of the flue leading from the furnace, not shown, wherein the flue gases to be cooled are generated. The heat exchanger is attached to the upper end of the flue I. As shown, the end of the flue is fitted into a central opening in the bottom sheet l2 of the heat exchanger. The heat exchanger comprises a sheet metal sleeve or drum 2 which, as shown in Fig. 3, is not quite circular, but has a contour constituting one turn of a spiral. The sleeve 2 extends downwardly below the bottom sheet I2 of the heat exchanger around the upper end of the flue l to provide an air intake passage 21 concentric with the flue l. The heat exchanger within the drum or sleeve 2 is formed of two spirally wound sheets of metal, one of which is a continuation of the sleeve 2 and constitutes the outside turn. The other sheet is indicated at 3 in Figs. 1, 2 and 3. The sheet 3 throughout its length and the sheet 2 except for the outside turn which forms the air intake of the heat exchanger are of a height to provide the necessary area of heat transfer surface with a length or linear horizontal dimension equal to, in the example shown, five convolutions of the spiral, the inner convolution of the sheet 3 having its smallest radius substantially equal to the radius of the flue section I. The bottom tube sheet 12 is fitted to the top of the flue I and a spiral slot 4 of a width equal to the space between the sheets 2 and 3 plus the thickness of the sheets is cut in the sheet [2. The lower edges of the sheets 2 and 3 are fitted in the slot 4 and brazed or welded to the edges of the spiral slot, as indicated at 22 in Fig. 1. An upper tube sheet l3 of similar de-' sign but with a closed central portion M is fitted and attached to the upper edges of the sheets 2 and 3, so that the only exit for the hot gases leaving the furnace in the flue l is horizontally into the space between adjacent turns of the spiral, as indicated by the arrow marked 5 in Fig. 2, and thence through the spiral passage to the discharge opening adjacent the outer edges of the sheets 2 and 3 as indicated by the arrow 6.

The air which enters the heat exchanger through the downwardly extending portion 2 of the outer wall of the spiral passes vertically upward through the spiral slot 4 in the tube sheet l2 and thence through the heat exchanger, as

indicated by the arrows I in Fig. 1 in the alternate spaces between the sheets 2 and 3 makin up the spiral. The adjacent vertical edges of the sheets 2 and 3 at the ends of the spiral slots in the tube sheets are connected by vertical strips l5 brazed or welded to the edges of the sheets 2 and 3. By this structure there is provided an extended spiral passageway for the flue gases leavingthe furnace anda vertical passageway for the air to be heated through the spiral in a direction parallel with the axis of the spiral.

The hot gases leave the space between. the: sheets making up the spiral in a horizontal direction, while the air which passes vertically through the heat exchangeriscaught hy'a' hood-9" which is fitted over the upper edge of the outer turn of the sheet which is extendedsspirallyfabnvethe upper tube sheet as shown in Figs. 1 and 3. The hood 9 is connected to a flue lfi through which the heated air isiconveyed to the firebox of: the :fnrna'cef or." to other: points; of use. If: the heated. air? is used: ascombustiom air? ini the furnace, a blower, as indicated iniFigzl-gis pref erablyprovidedtoi create; a forced draft-liar the furnace and also to insure that the entering air has. sufficient' velocity for efiicienti heat" transfer.

If:. desired; the fiuefgasesfr'om' which' the heat has been. extracted maybe? discharged directly intoithe atmospherei-at a point corresponding with the outer'turnsofthe spiral, as indi'cate'd by the arrow 6'. However, .itis usually n'ecessary to convey hot-flue'g'ases to a stackgand t'o' that end I preferably 'providean. out'sid drum' H I of circular cross section whichisurronnds the entire apparatus and-wh'ose; upper-- edge Z- is fitted into a hoo'd l2 atta'chedto the 'fiu'e leading to the stacl ll- As shown in" Fig.1 1, the flue I0fbr the discharge-of heated airfromthei heat exchanger is turned to a horizontal position andaext'endsi through the wall ofv the flue: leading to therstack'; Toreduce the resistaneertoithe flowofithzafiuegasesthrough the spiral passage the g ases rriaybe-discharged into a horizontal fiue tangential to the outer wall ofithe: heatexchanger atrthe dischaige opening and: thence to a stack or otherl'discharger The" operation of. the: apparatus will be clear from the foregoing description. The hot gases from the furnace. which. are discharged within the i'nner turnzofthe spiraliportion of tliehe'at exohangerfa're' drawn by; the suction: of J the stack at'EhighNeI'ocity into the-spiral passageway-mine directionindicatedi by theiarrow sun-Fig 2; and are discharged into the outerhobd' I25 whence they press'upwardly througlt the hood-*- in'to th'e flue leading to thestaclf.

In heat e'xehangers' having entwined spiral p'as sages-as heretofore constructed; thepass'ages for both fluids are spiral and the; edges: of the spiral sheets constituting the heat transfer elements are fixedt at" their top andlbottorn edges-to transverse headers which hold the:sl'ieets aigainst' elongation' and contraction in the direction: of their length; Withmy' improved-r construction there areno'transverserheadersexceptthe narrow spiral strips which-form the topand bottom walls of 6 tions between the spiral sheets and the support ing structure.

Instead of making the exchanger of two sheets with separate end closures for the gas passage the two spirally wound sheets may have reversely extending marginal flanges which are welded together to form a closed spiral conduit with the intermediateispjace openiat 'the endsjor" the passage of the air stream.

In Figs. 4, 5 and 6 I have shown a slight modification of the structure above described wherein the heat: transfer surface is increased without increasing the overall dimensions of the exchanger? Tof-thii end the strip 3a forming the inner strip? of the two strips which form the spiral is provideda't intervals with ribs 25 extending parallelawithrthe axis of the spiral. The portionof the spiral formed by the sheet 2 is flat and serves, with the ribs 25 of the other sheet, to form a series of separate longitudinal vertical passages thrbugh'whioh the'air flows.

A fiirther modificationof the'structure'isshown in FigsiT-andhl A s hereshown, a series of soils or" wire" wound hel-icall'y in" a manner similar to elm-extension spring an'dLof a-len'gth-equal to the length of 'th'e' spiral gaspassage are stacked one orizanother in' the ga's pa'ssage'to thus'greatly increase the metal-surfae'eavailable for the absorption of heat from-the gases.

The-heat absorbed bythe'coils of wire is transmitted as radiant heat' and also to some extent by conduction to" the metal walls of the spiral gas passage and thus serves to increase the ternperature of thesewalls and thereby increasethe heattransferred tothe air passing upwardly through the-intermediate passages.

Instead: of providing the alternate partition sheets with vertical ribs to increase the heat transfer surfacein' the' m'anner'shown in Fig. 4, one of thetwo 'sheets fonexample sheet 3, may be forrn'ed with lior i'zontalcorrugations as shown at 30 in' Figs: 9- and 1'0 By this arrangement an efiective extended heat transfer surface is prov ide'd fo'rthe fl'u'e g-as'es or other gases traveling spirally through the heat exchanger.

Also} ifdesired; both spiral sheets may be formed with corrugations; asshown' in-Figs. 11 and 121' thereby providingeffective extended heat transfehsurfacesfor b'othg'ases;

WhiI'eI haV'e desorilciedmy improved'heat exchanger a'suse'd fbr the-transferof heat from hot flue gases to air; it will be" understood that this is but a typical us'eof theapparatus and-that the heat e'xchang'ermay heusedwith like advantage? for the exchange of heat between gases and vapor's'of any character? It will'also be understood that whereas the heat exchanger is primarily designed 'fbr transfer of h'eatf'rom one aseous medium to another; it may also be used for the transfer of heat Between liquids or be tween a gaseous medium and a liquid medium, and tliatthe liduidmedium may be circulated through either the vertical passages alcove. described as airpa'ssa'gesor through the spiral. passage through which, in the above desc'rib'edinstalla-tion, fluegases" are; circulated. It will also be understood thatin addition to the modified structures herein illustratedvarious other modi ficatio'n's of the design may bemad'e' without departing from the spirit of the invention as, defined in=the'appended clai'ms? l claiin'z" I l: A heatexchangerforpreheating"combustion air by extracting heat from flue gas comprising in? c'ombination' a pair of entwined spiral plates heat exchange relation with each other, a central generally cylindrical chamber within said spirals,

a central inlet conduit for flue gas coaxial and communicating with said chamber, a lower seal ing sheet surrounding said conduit and closing off one of the spiral gaps between said plates at the bottom thereof, a cylindrical outer shell sealed to the lower sealing sheet enclosing said plates, a downwardly depending circumferentially continuous extension of the outermost wall of said plates substantially concentric with and surrounding said plates, an upwardly extending circumferentially continuous extension of the outermost wall of said plates, an upper sealing sheet within said upward extension sealing the top of said chamber and the spiral gap at the top of the lates forming the passageway which is sealed by said lower sheet, an exhaust stack for flue gas sealed to the top of said outer shell, and a delivery pipe for heated air sealed to the top of said upward extension, whereby flue gas entering the chamber from the conduit moves spirally outward through the passage formed between the upper and lower sheets to the space between the shell and the plates and thence upward to the stack and the air entering the downwardly depending extension moves axially upward between the unsealed plates into the upwardly extending extension.

2. A heat exchanger as set forth in claim 1 in which one of said entwined spiral plates forming the air passage is provided with axially extending ribs for increasing its heat transfer surface.

3. A heat exchanger as set forth in claim 1 in which one of said entwined spiral plates forming sage is provided with circumferentially extending ribs for increasing its heat transfer surface.

PHILIP S. O-TTE'N.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 9,690 Tillman Apr. 26, 1853 731,469 Pontois June 23, 1903 747,072 Human Dec. 15, 1903 1,056,932 Olson et al Mar. 25, 1913 1,654,294 Ljungstrom Dec. 27, 1927 1,823,481 Zander Sept. 15, 1931 2,470,860 Parrish May 24, 1949 

